Revision connector for spinal constructs

ABSTRACT

An extender system is configured to couple a vertebral bone anchor that has been previously implanted in a vertebra, or is newly implantable in a vertebra, to an adjacent bone, which can be an additional spinal level or an occiput, for example. The extender system includes an extension member having a body and an engagement member coupled to the body. The extension member defines an aperture extending through the engagement member. A screw is configured to attach the extension member to the vertebral bone anchor. The extension member can be fastened to the adjacent bone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.12/817,920, filed Jun. 17, 2010, which claims the benefit of U.S.Provisional Application Ser. No. 61/187,902, filed Jun. 17, 2009, thedisclosures of both of which are hereby incorporated by reference as ifset forth in their entirety herein.

TECHNICAL FIELD

The present disclosure relates generally to orthopedics, and inparticular relates to implants and methods for extending existingposterior vertebral screw assemblies to additional levels.

BACKGROUND

The options that exist for revising and/or extending a posteriorvertebral screw and rod construct in a patient are limited. Patients whohave undergone previous spinal surgery often develop symptoms inadjacent spinal levels, which often cause pain and require additionalsurgery. Such additional spine surgeries often require existing hardwareconstructs to be extended one or more additional spinal levels. In suchcases, a surgeon must decide if he can 1) extend the construct using thesame hardware as the patient's existing hardware, 2) extend theconstruct using different hardware while leaving some of the patient'sexisting hardware in tact, or 3) remove all of the patient's existinghardware and replace it with new hardware, including the new spinallevels to be instrumented. Several disadvantages, however, characterizethese approaches.

First, the patient's existing hardware must be identified via X-rays orfluoroscopy and, once identified, the surgeon must determine if the samemake and model of hardware is available to the hospital or still on themarket. The surgeon must also determine if his experience will allow himto revise and the existing hardware and/or add on new hardware, as someexisting hardware systems are more difficult to revise or install. Basedon these determinations, the surgeon may decide to revise using newhardware. Although a surgeon can choose the hardware of his choice, aconnection between the existing hardware and the new hardware must bemade, most often accomplished by creating a long incision long enough touncover all previously fixed vertebral bodies along with the newvertebral body or bodies to be fixed, removing the underlying rod,implanting the new screws, and then inserting a new rod to thepreviously implanted rod and the newly implanted rod. Concerns exist,however, that such a technique may disturb certain spinal levels thatwere previously asymptomatic and, thus, results in pain that previouslydid not exist. Further, many verterbal screw systems are not compatiblewith one another, significantly limiting the new hardware options foradding to the existing construct. If the surgeon decides to remove allexisting hardware and replace it with new hardware of his choice heagain is disturbing some spinal levels that were previouslyasymptomatic. Each of these options for adding and replacing hardware istime-consuming, especially if the surgeon is unfamiliar with thepatient's existing hardware.

SUMMARY

In accordance with one embodiment, an extender system is configured tobe operatively coupled to a vertebral implant that is secured to avertebra, the vertebral implant including a first bone anchor and afirst anchor seat that receives the first bone anchor. The extendersystem includes an extension member including a body and an engagementmember coupled to the body. The extender system further includes afastener that is configured to couple the extension member to thevertebral implant. The extender system further includes a second boneanchor that is configured to attach the extension member to anunderlying bone disposed adjacent the vertebra.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the application, will be better understood whenread in conjunction with the appended drawings. For the purposes ofillustrating the revision connector devices of the present application,there is shown in the drawings preferred embodiments. It should beunderstood, however, that the application is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1A is a perspective view of a bone fixation assembly constructed inaccordance with one embodiment including a plurality of bone fixationelements connected to a previously implanted spine fixation rod, andillustrated schematically as each being previously secured to avertebra;

FIG. 1B is a perspective view of one of the bone fixation elementsillustrated in FIG. 1A constructed in accordance with one embodiment,including an anchor seat, a bone anchor, a collet, and a locking cap;

FIG. 2 is a perspective view of the spine fixation rod illustrated inFIG. 1A;

FIG. 3 is a perspective view of the bone anchor illustrated in FIG. 1B;

FIG. 4 is a perspective view of the anchor seat illustrated in FIG. 1B;

FIG. 5A is an exploded perspective view of the locking cap illustratedin FIG. 1B;

FIG. 5B is a top plan view of the locking cap illustrated in FIG. 5A;

FIG. 5C is a sectional side elevation view of the locking capillustrated in FIG. 5B;

FIG. 6 is a perspective view of the collet illustrated in FIG. 1B;

FIG. 7A is a sectional side elevation view of the bone fixation elementillustrated in FIG. 1B taken along line 7A-7A, with the locking capremoved, to illustrate a vertebral screw assembly;

FIG. 7B is a sectional side elevation view similar to FIG. 7B, butshowing a spine fixation rod extending through the anchor seat, and alocking cap affixed to the anchor seat;

FIGS. 8A-D are schematic views illustrating a method for assembling thebone fixation element illustrated in FIG. 1A;

FIG. 9 is a perspective view similar to FIG. 1A, but showing a pluralityof superior and inferior vertebrae with respect to the previouslysecured vertebrae;

FIG. 10A is an exploded view of an extender system constructed inaccordance with one embodiment;

FIG. 10B is a sectional view through a portion of the extender systemillustrated in FIG. 10A;

FIG. 10C is a perspective view of the extender system illustrated inFIG. 10A coupled to a previously implanted bone fixation assembly;

FIG. 10D is an enlarged side elevation view of a portion of the extendersystem illustrated in FIG. 10A coupled to a previously implanted bonefixation assembly;

FIG. 11A is an exploded view of a cascading extender system to beimplanted into a plurality of vertebrae;

FIG. 11B is a perspective view of a pair of rows of the cascadingextender system illustrated in FIG. 11A implanted into the vertebrae;

FIG. 11C is a perspective view of parallel rows of fixation elementsconnected by a cross bar;

FIG. 11D is a perspective view of the fixation elements connected by across bar and implanted into a plurality of schematically illustratedvertebrae

FIG. 12 is a perspective view of the extender system illustrated in FIG.10A, but including an extension member constructed in accordance with analternative embodiment;

FIG. 13 is a perspective view of the extender system illustrated in FIG.10A, configured to connect a bone fixation element to apreviously-implanted translaminar screw;

FIG. 14A is a perspective view of a pair of the extender systemsillustrated in FIG. 10A configured to connect an occiput to a spine;

FIG. 14B is another perspective view of one of the extender systemsillustrated in FIG. 14A;

FIG. 14C is a perspective view of the extender systems illustrated inFIG. 14A connected between an occiput and a spine; and

FIG. 14D is another perspective view of one of the implanted extendersystems illustrated in FIG. 14C.

DETAILED DESCRIPTION

Certain terminology may be used in the following description forconvenience only and should not be considered as limiting in any way.For instance, a bone fixation assembly 20 includes one or more bonefixation elements 22, and four bone fixation elements 22A-D asillustrated in FIG. 1A. As shown in FIG. 1B, each bone fixation element22 extends vertically along an axial direction A, and generallyhorizontally along a radial direction R that extends perpendicular tothe axial direction A. Thus, the radial direction R includes alongitudinal direction L and a lateral direction LA that extendsperpendicular to the longitudinal direction L. It should be appreciatedthat the directional terms “longitudinal,” “lateral,” can likewise applyto the bone fixation assembly 20 as extending horizontally, and thedirectional term “transverse” can refer to a vertical direction. Thebone fixation element 22 defines an upper or posterior end 21 and alower or inferior end 23, such that the directional terms “upper” and“lower” and derivatives thereof refer to a direction from the lower end23 towards the upper end 21, and from the upper end 21 towards the lowerend 23, respectively.

The words “inward,” “outward,” “upper,” “lower,” “distal,” and“proximal,” refer to directions toward or away from, respectively, thegeometric center of the bone fixation assembly 20 and its components.The words, “anterior”, “posterior”, “superior,” “inferior” and relatedwords and/or phrases designate preferred positions and orientations inthe human body to which reference is made and are not meant to belimiting. It should further be appreciated that while round structuresdefine diameters as described herein, the round structures could bereplaced with alternative (e.g., polygonal) structures which woulddefine alternative cross-sectional dimensions opposed to diameters. Theterm “diameter” as used herein is intended to include all suchalternatives unless otherwise specified. The terminology includes theabove-listed words, derivatives thereof and words of similar import.

It should be appreciated that the directional terms are used herein withreference to the orientation of the bone fixation assembly 20 and itscomponents as illustrated, and that the actual orientation of the bonefixation assembly 20 and its components may change during use. Forinstance, the axial direction is illustrated as extending along avertical direction, and the radial direction is illustrated as extendingalong a horizontal direction, however the directions that encompass thevarious directions may differ during use, depending, for instance, onthe desired orientation of the bone fixation assembly 20 during use.Accordingly, the directional terms are used herein merely for thepurposes of clarity and convenience only, in a non-limiting manner.

Referring now to FIG. 1A, the bone fixation assembly 20 includes aplurality of bone fixation elements, such as bone fixation elements22A-D, connected by a spine fixation rod 24 that extends along alongitudinal axis L. The bone fixation elements 22A-D each include abone anchor 30 that is implanted (e.g., screwed) into a correspondingvertebra 27A-D. The bone fixation elements 22A-D can be implanted intothe posterior region of the spine, or any suitable alternative region ofthe spine, for instance into the pedicle or other spinal region. Thebone anchor 30 can be provided as a screw, hook, or alternativelyconstructed top loading bone anchor configured to attach to anunderlying vertebra. Unless otherwise specified, the bone fixationassembly 20 and its components can be made fromtitanium-aluminum-niobium alloy (TAN), implant-grade 316L stainlesssteel, or any suitable alternative implant-grade material.

With continuing reference to FIG. 1A, the bone fixation elements 22A-Dwill be described as and may be generally implanted in the spine, forinstance at the posterior portion of a lumbar, thoracic, or cervicalvertebral body. In this regard, when the bone fixation elements 22A-Dare joined by the rod 24, the assembly 20 fixes the relative position ofthe vertebrae (illustrated schematically at 27A-D). Accordingly, thebone fixation elements 22A-D can be referred to as vertebral implants,the spine fixation rod 24 can be referred to as a spine fixation rod,and the bone fixation assembly 20 can be referred to as a vertebralimplant. However, it should be appreciated that the bone fixationassembly 20 can also be used for fixation of other parts of the body,such as joints, long bones, or bones in the hands, face, feet,extremities, cranium, and the like.

As shown in FIG. 2, the spine fixation rod 24 is elongate along alongitudinal axis L, and includes a body 25 that is cylindrical ortubular in shape. The longitudinal axis L extends generally in acranial-caudal direction when the bone fixation assembly is affixed tothe spine. The rod body 25 may include, but is not limited to, a solidbody, a non-solid body, a flexible or dynamic body, or the like, and canassume any alternative shape as desired. It should thus be appreciatedthat the bone fixation assembly 20 is not limited in use to anyparticular spine fixation rod 24.

Referring now also to FIG. 1B, the bone fixation elements 22 a-d of thebone fixation assembly 20 will now be described with respect to the bonefixation element 22. In particular, the bone fixation element 22generally includes a vertebral implant 75, and a locking cap 34. Thevertebral implant 75 is illustrated as including a bone anchor seat 26,a collet 28 disposed inside the anchor seat 26, a bone anchor 30 (shownas a threaded bone screw) having a head portion 33 (see FIG. 3) attachedto the collet 28. The locking cap 34 is installed in the anchor seat 26at a location above the collet 28, such that the spine fixation rod 24is located in a rod slot 36 that is disposed, and as illustrateddefined, between the collet 28 and the locking cap 34.

Referring also to FIG. 3, the bone anchor 30 is configured as a bonescrew, or vertebral screw, that includes an externally threaded shaft 31coupled at its upper end to an enlarged curved head 33. The shaft 31extends axially along a central axis B of rotation, and can define anysuitable diameter, length, and thread design so as to engage theunderlying bone, such as a vertebra 27. Alternatively, the shaft 31 canbe unthreaded so as to define a pin or a nail if desired. Thus, oneskilled in the art will appreciate that the bone anchor 30 is notlimited to any particular type of shaft 31. The bone anchor 30 may alsobe cannulated and fenestrated such that openings extend radially outwardfrom a central hollow channel in a cannulated shaft to urge fluid out ofthe bone anchor 30 during injection or draw fluid into the centralhollow channel from the radial sides of the anchor during extraction ofmaterial adjacent the anchor if desired.

The bone anchor 30 further includes a vertically extending neck 35connected between the shaft 31 and the head 33. The neck 35 isillustrated as extending axially in a direction parallel to axis B, andincludes an outer neck surface 37 that defines a neck diameter, which isless than the diameter of the head 33.

The head 33 can define at least a partially spherical curvature, such asa semi-spherical curvature, or can alternatively define any suitablecurvature as desired to facilitate rotation with respect to the collet28 as is described in more detail below. The head 33 also includes adrive surface 39 configured to receive a corresponding tip of a drivetool, such as a screw driver configured to rotate the bone anchor 30into engagement with the vertebrae 27 or other underlying bone surface.The drive surface 39 can define a hexagon, a star drive pattern, aPhillips head pattern, a slot for a screw driver, threads configured toreceive corresponding threads of a threaded drive post, or any suitabledrive tool engaging structure as desired.

Referring now to FIG. 4, the anchor seat 26 includes an anchor seat body38 that can be described as a generally cylindrical tubular bodyextending centrally along an axial axis A that extends generally in theanterior-posterior direction when the bone fixation element is implantedin the underlying vertebra. The body 38 includes a base 40 and a pair ofspaced opposing arms 42 extending out (up in illustrated theorientation) from the base 40. The arms 42 can be substantiallyidentically or identically constructed. The arms 42 define correspondingupper ends 46 that are also the upper ends of the body 38, and define anupper opening 48. The base 40 defines a lower end 50 that is also thelower end of the body 38, and defines a lower opening 52. The body 38defines an axial bore 54 extending from the lower opening 52 to theupper opening 48.

The body 38 includes opposing support walls 56 and a pair of spacedopposing spacer walls 58 connected between the support walls 56. Thesupport walls 56 can be substantially identically or identicallyconstructed, and the spacer walls 58 can likewise be substantiallyidentically or identically constructed. The arms 42 extend up fromrespective support walls 56, and can be shaped as desired. Asillustrated, the arms 42 are arc-shaped with the axis of the arc passingthrough the plane of symmetry that bisects the anchor seat 26. Each arm42 extends circumferentially about its axis less than 180°, such asbetween 60° and 150°, for instance approximately 90°. For instance, eacharm 42 can extend circumferentially 90.5° about its axis.

Accordingly, a gap G extends circumferentially between adjacentcircumferentially outer ends of the arms 42. The opposing gaps G are inalignment with the axial bore 54. The arms 42 can be disposed radiallyopposite each other such that the gaps G, in combination with thealigned portion of the axial bore 54, define a rod-receiving channel 36that is sized and configured to receive the spine fixation rod 24 suchthat the spine fixation rod 24 extends through the bone fixation element22. Thus, the gaps G are aligned in the longitudinal direction. Thespine fixation rod 24 can thus extend through the opposing gaps G andthe axial bore 54. The arms 42 define radially inner and outer surfaces60 and 62, respectively. The inner surfaces 60 define threads 62, andare configured to threadedly receive the locking cap 34, as will now bedescribed.

In particular, referring to FIGS. 5A-C, the locking cap 34 isillustrated as a set screw 64 and a saddle 66 operatively coupled to theset screw 64. The set screw 64 includes a generally cylindrical setscrew body 65 having external threads 68 configured to threadedly engagethe threads 62 formed on the inner surfaces 60 of the arms 42. Inaccordance with one embodiment, the threads 68 and 62 can incorporateinclined load flanks forming an angle with respect to the axis A of thebone fixation element 22. The load flanks may converge so that the topsurface of the thread and the bottom surface of the thread converge. Theangle may be between 0 degrees (0°) and 30 degrees (30°), and in oneembodiment can be about five degrees (5°). One skilled in the art willappreciate that the threads may take on any alternative form as desired,including negative load threads, perpendicular threads, buttressthreads, or the like.

The externally threaded set screw 64 generally provides flexibility wheninserting the spine fixation rod 24 into the anchor seat body 38 suchthat the spine fixation rod 24 need not be completely reduced or seatedwithin the body 38 prior to engagement of the locking cap 34. The setscrew 64 is configured to be tightened within the anchor seat 26 againstthe spine fixation rod 24. The locking cap 34 may be constructed asdesired for this purpose including, but not limited to, an externallythreaded cap, a quarter-turn or partial-turn locking cap, a two-piecescrew set, or the like.

The set screw 64 is illustrated as including a drive surface 70 providedas an internal recess extending vertically down into the upper end ofthe screw 64. The drive surface has any suitable shape configured tocooperate with a corresponding drive tool for threadedly securing theset screw 64 onto the anchor seat body 38. The drive surface 70 candefine any shape as desired, for instance an external hexagon, a stardrive pattern, a Phillips head pattern, a slot for a screw driver, athreading for a correspondingly threaded post, or the like.

With continuing reference to FIGS. 5A-C, the saddle 66 includes a saddlebody 72 having a transverse recess 74 extending up into the bottom endof the saddle body 72. The recess 74 can define a round surface thatextends about a longitudinally extending axis, such that the recess 74is configured to receive the spine fixation rod 24 at a rod-contactingsurface 76. The rod-contacting surface 76 can include a desired surfacefinish that adds roughness, such as, for example, a knurl, beadblasting, grooves, or other textured finish that increases surfaceroughness and enhances rod push through strength.

The saddle 66 can be coupled to the set screw 64 in any desired manner,including adhesion, mechanical fastening, and the like. In theillustrated embodiment, the saddle 66 includes a stem 78 extendingcentrally upward from the saddle body 72. The stem 78 is configured tobe received in a central bore 32 extending vertically into the lower endof the set screw body 65, and can be fastened within the central borewith a rivet 80 or other like fastener. Accordingly, the saddle 66 isrotatable relative to the set screw 64, such that the saddle 66 canself-align with the spine fixation rod 24 as the set screw 64 is beingrotated with respect to the anchor seat 26, for instance when thelocking cap 34 is being tightened against the spine fixation rod 24.

Referring again to FIG. 4, and as described above, the anchor seat body38 includes a pair of spaced opposing support walls 56 and a pair ofspaced opposing spacer walls 58 connected between the support walls 56.The arms 42 extend up from respective support walls 56, such that thespacer walls 58 are disposed between the arms 42. Each of the spacerwalls 58 defines opposing upper ends 84 and lower ends 82 that can beshaped as desired. The upper ends 84 are round in accordance with theillustrated embodiment, such that the upper ends 84 and thecircumferentially outer ends of the arms 42 are adjoined to generallydefine a U-shape from a horizontal view through the gaps G. Thus, theupper ends 84 define the lower end of the gaps G.

The upper ends 84 can be shaped to conform generally with the outersurface of the spine fixation rod 24, such that the upper ends 84receive and engage the spine fixation rod 24 during use. Alternatively,the upper ends 84 can be spaced slightly below the upper surface of thecollet 28, such that the collet 28 supports the spine fixation rod 24during use, as will be described in more detail below.

The support walls 56 each define opposing inner and outer surfaces 86and 88, respectively. The support walls 56 and the spacer walls 58 flareinward toward the central axis A in a downward direction from the arms42, and terminate at respective lower ends 90. The inner surfaces 86 ofthe opposing support walls 56 and spacer walls 58 at the lower end 90define a distance D therebetween that is less than the distance betweenopposing radially opposing inner surfaces 60 of the arms 42. Thedistance D can be less than or greater than the diameter of the head 33of the bone anchor 30. The inner surfaces 86 flare radially inwardtoward the central axis A, and toward each other, along a downwarddirection, and are each connected to bottommost, and innermost, surfacesthat define respective abutment walls 92.

Referring also to FIGS. 4B and 7A, each abutment wall 92 definesrespective inner abutment surfaces 93 that in turn define a distancetherebetween that is substantially equal to the diameter of the neck 35,such that the abutment walls 92 are configured to abut opposing abutmentsurfaces of the bone anchor, which are illustrated as opposing sides ofthe outer neck surface 37 when the bone anchor 30 is disposed in theanchor seat 26. Thus, the abutment walls 92 can prevent or limitpivoting of the bone anchor 30 relative to the anchor seat 26 in adesired plane.

Referring now to FIG. 6, the collet 28 includes a collet body 45 thatdefines a first or upper end 47 sized and configured to contact orsupport at least a portion of the spine fixation rod 24 when the rod isreceived within the rod-receiving channel 36, and a second or lower end49 sized and configured to contact or otherwise engage, directly orindirectly, a portion of the bone anchor head 33. The collet body 45 isannular, and thus defines an axial bore 53 extending between and throughthe upper and lower ends 47 and 49. The axial bore 53 is aligned withthe axial bore 54 when the collet 28 is installed in the anchor seat 26.

Referring to FIGS. 6 and 7A-B, the upper end 47 defines radiallyopposing upwardly facing seat portions 51 having a curvature orsemi-spherical shape corresponding to the outer surface of the spinefixation rod 24, and is therefore configured to receive or otherwisesupport at least a portion (e.g., a lower portion) of the rod 24. Thelower end 49 defines an inner surface 55 defining a curvature orsemi-spherical shape corresponding to the outer surface of the anchorhead 33, and is therefore configured to receive or otherwise engage atleast a portion of the head 33, so that the head can rotate with respectto the collet 28 and the anchor seat 26, and can further pivot withrespect to the collet 28 as permitted by the anchor seat 26. Because thebone anchor 30 can freely rotate about its axis of rotation B relativeto the anchor seat 26, and thus the anchor seat 26 can likewise rotateabout the bone anchor 30, the rod-receiving channel 36 can be alignedwith the spine fixation rod 24 without advancing or withdrawing the boneanchor 30 in or out of the underlying bone. Thus, the bone anchor 30 canmaintain a constant insertion depth in the underlying bone (e.g.,vertebra 27) while adjusting the orientation of the rod-receivingchannel 36.

The collet 28 further includes a pair of flanges 57 extending up fromthe upper end 47 of the collet body 45 at a location radially betweenthe seat portions 51. A locking lip 59 extends radially out from eachflange 57. As best shown in FIG. 7A, the anchor seat 26 defines a pairof opposing recesses 61 (see FIG. 8A) formed radially in the opposinginner surfaces 86 of the support walls 56 at a location below thethreaded inner surfaces 60 of the arms 42. During operation, the collet28 can be inserted down into the anchor seat 26, thereby causing theflanges 57 to flex inwardly past the threaded inner surfaces 60, untilthe lips 59 clear the upper ends of the recesses 61, at which point theflanges 57 snap back out so that the lips 59 are disposed in therecesses 61. Interference between the lips 59 and the upper ends of therecesses 61 prevent the collet 28 from backing out through the upper endof the anchor seat 26. The recesses 61 further define a circumferentiallength substantially equal to that of the flanges 57 and locking lips59, such that the collet 28 is rotationally fixed with respect to theanchor seat 26 in a position whereby the upper surface 47 is alignedwith the spine fixation rod 24 when the spine fixation rod 24 isinserted into the anchor seat 26.

The lower end 49 of the collet 28 defines an outer diameter that isgreater than the inner distance between the abutment walls 92.Accordingly, the collet 28 is unable to pass axially down through thelower end of the anchor body 26. The lower end 49 includes one or moreslots 67 (illustrated as a plurality of slots) extending radiallytherethrough so as to define opposing pluralities of fingers 69 that areconfigured to pop over the head 33 of the bone anchor 30. When thecollet 28 is disposed in the anchor seat 26 such that the lips 59 aredisposed in the respective recesses 61, the fingers 69 are axiallyaligned with the abutment walls 92. Thus, as shown in FIGS. 7A-B, whenthe collet 28 and anchor 30 are installed in the anchor seat 24, thefingers 69 radially expand to conform to the outer surface of the anchorhead 33 and the inner surfaces of the anchor seat 26. The innerdiameters defined by the opposing fingers 69 are less than the outerdiameter of the anchor head 33 to prevent the anchor 30 from beingremoved from the anchor seat 26 in an axially downward direction. Thelower ends of the fingers 69 terminate at a location above the abutmentwalls 92. Accordingly, the fingers 69 do not interfere with theengagement between the anchor neck 35 and the abutment walls 92.

Referring now to FIGS. 8A-D, a method for assembling the vertebralimplant 75 includes at step 1, inserting the bone anchor 30 verticallydown through the axial bore 54, such that the shaft 31 extends throughthe lower opening 52 of the lower end 50 of the anchor seat 26, and theanchor head 33 is disposed above the abutment walls 92. This method stepfor inserting the bone anchor 30 into the anchor seat 26 can thus bereferred to as top-end loading of the bone anchor 30 into the anchorseat 26. Next, at step 2, the collet 28 is inserted into the axial bore54 to a location whereby the locking lips 59 can engage the lowermostthreads 62 of the inner surface 60 of the arms 42. Next, at step 3, anupward force can be applied to the bone anchor 30 so as to insert theanchor head 33 into the lower end 49 of the collet 28. The locking lips59 of the collet 28 brace against the anchor seat 26 inside the threads62 to prevent the upward force applied by the screw 28 from causing thecollet 28 to back out of the upper opening of the anchor seat 26. Atstep 4, a downward force is applied to the collet 28, thereby insertingthe locking lips 59 into the recesses 61 in the manner described above,and locking the anchor 30 and collet 28 in the anchor seat 26.

During use, because the bone anchor 30 is rotatable with respect to thecollet 28 and the anchor seat 26, a driving tool can engage the drivesurface 39 of the head 33 so as to insert the threaded shaft 31 into theunderlying bone, as shown in FIG. 1A. Next, as shown in FIGS. 8A-D, theanchor seat 26 can be rotated about axis A in the direction of Arrow Rabout the full 360° range of angles so as to align the rod-receivingchannel 36 with the longitudinal axis of the spine fixation rod 24.Thus, the vertebral implant 75 can be referred to as a polyaxialvertebral implant, and the bone fixation elements 22 can be referred toas polyaxial bone fixation elements. Alternatively, it should beappreciated that the bone fixation element can allow the anchor seat 26to rotate in one plane with respect to the axis A, and can thus bereferred to as a monaxial vertebral implant. It should be furtherappreciated that the vertebral implant can include a hook as the boneanchor 30 as opposed to a screw. Once the bone anchor 30 has reached adesired depth in the underlying vertebra, the spine fixation rod 24 canbe inserted into the vertebral implant 75. In particular, the spinefixation rod 24 is inserted into the axial bore 54 either horizontallythrough the gaps G, or vertically down into the axial bore 54. It shouldbe appreciated that the spine fixation rod 24 will be seated in theupper end 47 of the collet 28.

With continuing reference to FIGS. 8A-D, once the rod 24 is installed inthe vertebral implant 75, the locking cap 34 can be attached to theassembly 75 so as to fully assemble the anchor assembly 22. In theillustrated embodiment, the external threads 68 of the set screw 64 arerotated within the inner threads 62 of the anchor seat arms 42, therebycausing the set screw and saddle 66 to move axially down in the axialbore 54. As the saddle 66 approaches the spine fixation rod 24, thesaddle 66 is rotated with respect to the set screw 64 so as to bring therod-contacting surface 76 into alignment with the spine fixation rod 24.Once the saddle 66 is aligned with the spine fixation rod 24, the setscrew 64 is continuously threadedly inserted into the bone anchor 26,such that the locking cap 34 can be tightened against the rod 24,thereby applying a downward axial force to the rod 24. The locking cap34 can be said to be in an initial position when installed in thelocking cap 34 but before applying an axial force against the spinefixation rod 24. The axial force applied to the rod 24 by the lockingcap 34 is transmitted to the collet 28, which causes the fingers 69 toride along the inner surfaces 86 of the support walls 56 and spacerwalls 58.

As the fingers 69 ride along the walls 56 and 58, they become radiallyinwardly displaced due to the inward flare of the inner surfaces of thewalls 56 and 58, thereby radially biasing, or radially compressing, thefingers 69 against the anchor head 33. Increasing radial compression ofthe fingers 69 against the anchor head 33 causes frictional forcesbetween the fingers 69 and the anchor head 33 that resist rotation ofthe anchor 30 about the axis A relative to the anchor seat 26, collet28, and spine fixation rod 24. When the locking cap is fully tightenedto a locked position, the resulting frictional forces prevent the anchor30 from movement relative to the anchor seat 26, collet 28, and spinefixation rod 24. Thus, the locking cap 34 is configured to transmit alocking force onto the collet 28 and bone anchor 30 to fix or lock theposition of the bone anchor 30 relative to the anchor seat 26 and spinefixation rod 24. It should thus be appreciated that the spine fixationrod 24 is thus implanted to the underlying vertebra that is engaged bythe bone anchor 30.

It should be appreciated that the above-described method steps can beperformed for each bone fixation element of the bone fixation assembly20 as desired. Furthermore, it should be appreciated that the while thebone fixation elements 22 a-d have been described as each including thevertebral implant 75 described above, the bone fixation elements 22 a-dcan include any alternatively constructed vertebral implant suitable forfixing the spine fixation rod 24 to the underlying vertebrae 27. Forinstance, the vertebral implant 75 can be constructed so as to permitthe bone anchor 30 to be implanted into underlying bone before theanchor head 33 is inserted into the collet 28. In one embodiment, theabutment walls 92 are slotted so as to expand over the anchor head 33.Accordingly, the anchor seat 26 and collet 28 can be popped onto thehead 33 from above instead of inserting the anchor 30 down through theanchor seat 26 in the manner described above. The method step of poppingthe anchor seat 26 over the head 33 can be referred to as bottom-endloading of the anchor 30 into the anchor seat 26. It should be furtherappreciated that while the bone fixation assembly 20, including the bonefixation elements 22 and vertebral implants 75, have been described inconnection with one embodiment, the bone fixation assembly 20, includingthe bone fixation elements 22 and vertebral implants 75, can beconstructed in accordance with any embodiment suitable to be implantedinto a plurality of vertebrae and be connected by a spine fixation rod,such as described in U.S. patent application Ser. No. 11/603,428, filedNov. 21, 2006, and published as U.S. Publication No. 2007/0118123,published on May 24, 2007, the disclosure of which is herebyincorporated by reference as if set forth in its entirety herein.

Referring now to FIG. 9, it should be appreciated that the while thespine fixation rod 24 is implanted in a plurality of vertebrae 27 a-d inthe bone fixation assembly 20, it may become desirable at a future dateto extend the bone fixation assembly 20 to affix at least one such as aplurality of vertebrae to the vertebrae 27 a-d. For instance, it may bedesirable to affix at least one such as a plurality of inferiorvertebrae 27 e-f to the vertebrae 27 a-d. Alternatively or additionally,it may be desirable to affix at least one such as a plurality ofsuperior vertebrae 27 g-h to the vertebrae 27 a-d. Thus, the spinefixation rod 24 can be referred to herein as a previously implantedspine fixation rod. As illustrated, the vertebra 27 a is thecranial-most vertebra that is secured to the spine fixation rod 24, andthe vertebra 27 d is the caudal-most vertebra that is secured to thespine fixation rod 24. The vertebra 27 h is superior to the vertebra 27a, and the vertebra 27 g is superior to the vertebra 27 h. The vertebra27 e is inferior to the vertebra 27 d, and the vertebra 27 f is inferiorto the vertebra 27 e. The vertebrae 27 g-h and 27 e-f can be referred toas new vertebrae.

Referring now to FIGS. 10A-D, an extender system 100 includes atop-loading polyaxial spinal construct extender 105 that is configuredto be operatively coupled to the spine fixation rod 24 of a previouslyimplanted bone fixation element 22 or newly implantable bone fixationelement so as to join one or more vertebrae, that have been joinedtogether using the bone fixation system 20, with an adjacent bone. Thusthe polyaxial spinal construct extender 105 can be configured to extendthe bone fixation system 20 to one or more adjacent spinal levels. Onehaving ordinary skill in the art will appreciate that the polyaxialspinal construct extender 105 is not limited to extending a constructthat has already been implanted and may be utilized in original spinalsurgeries, potentially in a minimally invasive manner, to fix multiplelevels of a patient's vertebrae.

The polyaxial construct extender 105 includes a polyaxial extensionmember 139 constructed as a rod 140 that having a substantiallycylindrical rod body 141 that defines a proximal end 141 a and anopposed distal end 141 b. The polyaxial extender rod 104 includes anengagement member illustrated as a loop 142 that is attached to theproximal rod body end 141 a, and an aperture 143 extending verticallythrough the loop 142. The distal end 141 b can be coplanar with the loop142 as illustrated. Alternatively, the distal end 141 b can be angularlyor otherwise vertically offset with respect to the loop 142. Thepolyaxial extender rod 140 further includes a bushing 150 disposedwithin the aperture 143, and secured to the loop 142. The extender 105further includes a tapered fastener illustrated as a tapered set screw130 configured to connect to both the bushing 150 and the anchor seat 26(either of the previously implanted bone fixation system 20 or of a newbone fixation system), and a locking member illustrated as a locking nut160 configured to lock the extender rod 104 to the set screw 130.

The tapered set screw 130 includes a proximal portion 130 a, a distalportion 130 b, and a middle portion 130 c disposed between the proximalportion 130 a and the distal portion 130 b. The set screw 130 includesat the proximal portion 130 a a non-tapered exterior surface having anexterior set of threading 131 that is configured to engage an interiorset of threading on the locking nut 160. The distal portion 130 b of thetapered set screw 130 includes a non-tapered exterior surface 132 havingan exterior set of threading 133 that is configured to engage a set ofinterior threading of the anchor seat 26. The set screw 130 includes atthe middle portion 130 c a tapered nonthreaded exterior surface 134 thatis configured to abut the interior surface 151 of the bushing 150. Thetapered exterior surface 134 is configured such that the circumferenceof the middle portion 130 c increases along a direction from theproximal portion 130 a toward the distal portion 130 b.

The bushing 150 includes a flat superior surface 152, a flat inferiorsurface 153, a central longitudinal axis 154 extending between thesuperior surface 152 and the inferior surface 153, and a partiallyspherical exterior surface 155 extending between the flat superior andinferior surfaces 152 and 153, and an interior surface 151 surrounding ahollow interior 156. The bushing 150 includes a split 157 extendingalong the longitudinal axis through the exterior and interior surfaces155 and 151 to allow the bushing to expand in circumference as thetapered middle portion 130 c of the tapered set screw 130 is driven intothe interior 156.

The interior surface 151 of the bushing 150 includes an inferior taper151 a and a superior taper 151 b, such that the inferior taper 151 aextends between the inferior surface 153 and a mid-point of the interiorsurface 151, while the superior taper 151 b extends between the superiorsurface 152 and the point of the interior surface 151. The point of theinterior surface 151 is generally the circular line at which the twotapers meet to form an apex 158. The inferior taper 151 a and thesuperior taper 151 b each preferably define an angle with respect to thelongitudinal axis 154 that matches the taper angle of the exteriorsurface 134 of the middle portion 130 c of the tapered set screw 130.

The bushing 150 is press fit into the aperture 143 of the loop 142 ofthe extender rod 140. The partially spherical exterior surface of thebushing 150 is generally similar or identical to the spherical geometryof the interior surface of the loop 142, such that the bushing 150 ispolyaxially rotatable within the aperture 143 in an initial state priorto insertion of the screw 130. Once the screw 130 is inserted into thebushing 150, the tapered exterior surface 134 of the screw 130 ridesalong the interior surface 151 of the bushing, can causes the split 157to expand, such that the exterior surface 155 of the busing is pressedagainst the interior surface loop 142, thereby locking the position ofthe bushing 150 inside the loop 142.

Referring now also again to FIG. 9, the system 100 can also include anewly implanted bone fixation element 22 g disposed at an adjacentvertebra, for instance the superior vertebra 27 g as illustrated, or theinferior vertebra 27 e. The polyaxial extender rod 140 provides thespinal fixation rod that extends through the anchor seat 26 of the newlyimplanted bone fixation element 22 g. Thus, the polyaxial extender rod140 is coupled between the newly implanted bone fixation element 22 gand another bone fixation element 22 a, which can be part of apreviously implanted bone fixation assembly 20.

Thus, during operation, the top loading polyaxial construct extender 105may be implemented to extend a previously implanted spinal construct orbone fixation assembly 20 that includes the previously implanted bonefixation element 22 a to an adjacent bone, illustrated as an adjacentspinal level, and create a rigid connection therebetween during revisionsurgery. An incision is made at the spinal level adjacent to, forexample adjacent to the most cranial (or most caudal), level of anexisting spinal construct in need of revision. The incision is made overthe outermost preexisting bone fixation element 20 and the new vertebraeto be fixed, and an incision need not be made across the other vertebrae27 a-27 d of the preexisting bone fixation element 20 because thepreexisting spine fixation rod 24 is not removed. The new bone fixationelement 22 g, with the exception of the locking cap 34, is implantedinto the adjacent spinal level 27 g. Otherwise stated, the vertebralimplant 75 of the new bone fixation element 22 g is implanted into theadjacent spinal level 27 g. Through the same incision, or using a secondincision, the locking cap 34 is removed from an outermost, such as thecranial most, bone fixation element 22 a (or caudal most bone fixationelement 22 d).

The tapered set screw 130 is then coupled to the previously implantedbone fixation element 22 a by screwing the threading 133 at the distalend 130 b of the tapered set screw 130 into the threading on theinterior of the anchor seat 26. Because the locking cap 34 of thepreviously implanted vertebral implant 22 a has been removed, it canalso be said that the tapered set screw 130 is coupled to the polyaxialvertebral implant 75 of the previously implanted bone fixation element22 a. The extender rod 140 is then connected between the previouslyimplanted polyaxial vertebral implant 22 a and the newly implantedvertebral implant 22 g by placing the bushing 150 retained within theloop 142 around the middle portion of the tapered set screw 130 and theopposite end of the extender rod 140 vertically down into the anchorseat 26 of the newly implanted bone fixation element 22 g. The sphericalexterior surface 155 of the bushing 150 and complementary sphericalinterior surface 147 of the loop 142 that defines the aperture 143allows the bushing 150 to rotate polyaxially within the aperture 143 ofthe loop 142. The doubly tapered interior surface 151 of the bushing 150allows orientational freedom in coupling the extender rod 140 to thetapered set screw 130, because the oppositely oriented tapers allow theextender rod 140 to be coupled to the tapered set screw 130 in eitherdirection, such that there is no incorrect orientation.

The locking nut 160 is then screwed down, e.g., by engaging aninstrument-engaging feature on the exterior or superior surface of thelocking nut 160, over the proximal or superior portion 130 a of thetapered set screw 130, forcing the extender rod 140 and the bushing 150to advance distally with respect to the middle portion 130 b of thetapered set screw 130 and, in so doing, forcing the bushing 150 toexpand and match tapers of the interior surface 151 and the exteriorsurface 134 of the middle portion 130 c of the tapered set screw 130 tolock via an interference fit. The locking cap 34 is then screwed intothe top of the anchor seat 26 until the angular orientation of the boneanchor 30 is locked with respect to the anchor seat 26 and the extenderrod 140 is secured in the bone fixation element 22. As illustrated inFIG. 10D, the extender rod body 141 can be substantially “s-shaped”,such that the proximal end 141 a is disposed posterior with respect tothe distal end 141 b. Alternatively, the extender rod 140 can besubstantially linear, or define a substantially constant or variablecurvature (see FIGS. 14A-C), and the bushing 150 can be oriented suchthat the proximal end 141 a is disposed posterior with respect to thedistal end 141 b. Thus, the proximal end 141 a can be installed abovethe pre-existing spine fixation rod 24, while the distal end 141 b canbe substantially aligned with the pre-existing spine fixation rod 24. Inthe case of the system 100 including parallel rows 101 a and 101 b offixation elements 22 and spinal construct extenders 105, theabove-described fixation procedure is repeated for the opposite row.

To extend a previously implanted bone fixation assembly 20 caudally, asopposed to cranially, the top-loading polyaxial spinal constructextender 105 is connected to the vertebral implant 75 of the inferiorbone fixation element 22 d in the manner described above, a new bonefixation element is secured in an inferior vertebra, such as vertebra 27e, and the extender rod 140 is connected between the vertebral implant75 of the inferior most pre-existing fixation element 22 and the newlyimplanted bone fixation element in the manner described above.

The top-loading capability of the system 100 enables less invasive, lessdifficult, and less time consuming revision surgeries to occur whencompared to conventional spinal revision surgery systems and methodsthat generally necessitate the entire previously implanted spinalconstruct to be disassembled and then reassembled with a longer rodusing another large incision with the potential for significant bloodloss in order to fuse an adjacent spinal level. The system 100 generallyreduces the necessary incision length and decreases surgical time, bloodloss, postoperative pain, and healing time. Further, the system 100 ofthe first preferred embodiment may enable minimally invasive techniquesto be utilized when constructing a multiple level spinal rod assembly asthe relatively short length of the extender rod 140 permits insertion ofmultiple fixation screws and extender rods 140 into a single smallincision, sequential stacking of the rods across multiple levels andrelatively easy manipulation of the extender rods 140 into engagementwith the fixation screws.

It should be appreciated that the rod 140 can include a dampeningmechanism so as to provide additional motion as desired, for instancebetween one portion of the rod 140 and the loop 142. In addition, therod 140 can be entirely made of an elastic material further providing adynamic connection between levels. For example, the rod body 141 and/orthe loop 142 can be constructed of a polyetheretherketone (PEEK)material that permits damping or limited motion between adjacentpolyaxial vertebral implants 75. The loop 142, rod 140, bushing 150,locking nut 160, set screw 130, spinal rod 42, anchor seat 26, and/orother components of the system 100 can be configured to limit theultimate movement of the components relative to each other to preventover-extension or over-compression of the components relative to eachother even if certain of the components are constructed to permit motionor to be dynamic.

Referring to FIGS. 11A-C, while the system 100 has been described forextending an existing construct to one adjacent spinal level, such assuperior vertebrae 27 g or inferior vertebra 27 e as illustrated, thesystem 100 can further include two or more top-loading polyaxialcascading construct extenders 105 and a corresponding number of newlyimplantable bone fixation elements 22, such that the system can be usedto attach multiple vertebrae that were previously not fixed. Forinstance, the polyaxial construct extender 105 can be attached to thenewly implanted bone fixation element 22 g in the manner describedabove, and a newly implanted bone fixation element 22 can be attached toan adjacent superior vertebral body 27 h in the manner described abovewith respect to the vertebral body 27 g. An extender rod 140 can then beconnected between the polyaxial construct extender 105 attached to thebone fixation element 22 g and the newly implanted bone fixation element22 that was implanted in the vertebral body 27 h. It should thus beappreciated that the cascading construct extenders 105 can be fixed tonewly implanted vertebral bodies 27 g and 27 h without being fixed to apreviously implanted fixation system.

The implantation of the cascading construct extenders can be minimallyinvasive, as a single incision can be made that accommodates acannulated tube at a single vertebral level, as opposed to creating anincision along all vertebral levels to be fixed. The implantation can beperformed at each vertebral level through a cannulated tube or retractorthat extends through the incision, and the tube can be pivoted or theretractor can be pivoted or expanded so as to provide access to theadjacent vertebral levels to be implanted with the cascading constructextender 105.

It should be appreciated, as illustrated in FIG. 11A, that the cascadingextender system 100 can be include only top loading polyaxial constructextenders 105 alone or in combination with a corresponding plurality ofpreviously implanted bone fixation elements 22. The plurality ofindividual extender rods 140 substitute for the spine fixation rod 24and the polyaxial bushings 150 retained within the loops 142 as desiredso as to provide the desired angular adjustment capabilities and allowfor top loading connections to the anchor seats 26 of the newlyimplantable bone fixation elements 22.

The conventional cervical spine surgical art typically utilizes hooksthat generally require a first shallow trajectory to anchor the hookinto bone and then a second, vertical trajectory to couple the hook to aspinal rod 120. The two disparate trajectories may necessitate a largeincision for accessing the surgical site. The operational method forusing the system 100 illustrated in FIG. 11A generally requires only onetrajectory to implant each newly implantable bone fixation element 22and top loading polyaxial construct extender 105, introduce the extenderrod 140, and finally tighten the locking nut 160. Accordingly, thesystem 100 of the third preferred embodiment permits percutaneous stabincisions or one small incision to be utilized instead of a largeincision. The trajectory for use during the implantation of the system100 may be similar to the widely used Magerl technique and trajectory.

As illustrated in FIGS. 12A-B, the system 100 can further include one orboth cross connectors 190 and 193 that are configured to join the rows101 a and 101 b. The cross connector 190 includes a transverse connectorrod 191 and a clamp 192 connected to the opposing ends of the rod 191that are each configured to receive and secure to the spine fixation rod24 of the rows 101 a and 101 b. The cross connector 193 includes atransverse connector rod 194 that defines a pair of rod segments 194 aand 194 b that can be joined together using any suitable mechanicaljoint 195. The transverse connector rod 194 includes a first loop 196 adisposed at the outer end of the first rod segment 194 a, and a secondloop 196 b disposed at the opposed outer end of the second rod segment194 b. Each loop 196 a-b can be constructed as described above withrespect to the loop 142 of the extender rod 140. Thus, the system 100can include a spinal construct extender 105′ modified with respect tothe spinal construct extender 105 in that the cross connector 193replaces the extender rod 140. The modified spinal construct extender105′ can be attached to the outermost bone fixation elements 22 in themanner described above, such that the transverse connector rod 194 isconnected between the outermost vertebral implants 75 of the rows 101 aand 101 b.

Referring now to FIG. 13, it should be appreciated that the top-loadingpolyaxial construct extender 105 can be constructed in accordance withan alternative embodiment. In particular, the extender 105 can beconstructed as described above, however the extension member 139 isconstructed as a plate 180 having a plate body 181 that defines aproximal end 181 a, a distal end 181 b that is opposite the proximal end181 a along a central longitudinal axis 185, and a middle portion 181 cdisposed between the proximal end 181 a and the distal end 181 b. Thedistal end 181 b can be pivotally movable about arrow 187 with respectto the middle portion 181 c so as to conform to the anatomicaltopography of the underlying bone to be fastened. The plate body 180includes an engagement member illustrated as a loop 182 that isconnected to the proximal end 181 a. The loop 182 is constructed asdescribed above with respect to the loop 142 of the rod 140, such thatthe bushing 150 is retained within the loop 182 in the manner describedabove.

The plate 180 defines a plurality of apertures 183 that extend throughthe middle portion 181 c and the distal end 181 b, and are thuslongitudinally spaced along the length of the plate body 181. Theapertures 183 are each configured to receive a bone fastener, such asthe bone fastener 30 described above, which can be compressive screws orlocking screws, so as to secure the plate body 181 directly to anunderlying bone, such as a vertebral body 27 or a lamina. The apertures183 can include at least one circular aperture 184 sized to receive thebone fastener in a fixed position, and at least one longitudinallyelongate aperture or slot 186 sized to receive the bone fastener suchthat the bone fastener is translatable within the slot 186 so as toassist with alignment of the bone fastener and the underlying bone priorto securing the bone fastener against the plate body 181. Alternatively,the slot 186 can retain bone graft material that is inserted into theplate body 181 during a laminoplasty procedure. In accordance with theillustrated embodiment, the extension plate 180 is malleable to allowsome preoperative or intraoperative adjustment of the plate bodygeometry. One or more, up to all of the apertures 183 can be unthreadedso that the anchor 30 can compress the plate against the underlyingbone, or one or more up to all of the apertures 183 can be threaded sothat the bone anchor 30 can present complementary threads that mate withthe threads of the apertures 183 so as to fix, or lock, the plate 180 tounderlying bone without compressing the bone against the underlyingbone.

During operation, the extender 105 is coupled to a previously implantedor newly implanted or newly implantable polyaxial bone fixation element22 in the manner described above. The second end of the extension plate180 can be anchored to bone directly, such as the lamina arch of avertebral body. The top loading polyaxial plate extender 105 includingthe extension plate 180 is generally configured to contain graft,especially with open door laminoplasty procedures (such that theunderlying bone is allograft) and/or with longer cervical-occipitalfusion constructs. For instance, the plate 180 can be placed over thevertebral bodies 27 to be fixed, and the bone anchors 30 of the bonefixation elements 22 can be inserted through the complementary apertures183 so as to fix both the fixation elements 22 and the plate 180 to theunderlying vertebrae 27. Thus, the plate provides the ability to combinea laminoplasty procedure with a posterior fusion procedure using asingle construct. Conventional constructs typically utilize cabling tocontain such grafts, and the extension plate 180 provides a generallymore rigid method of graft containment, and the top loading polyaxialcoupling capabilities provided by the extender 105 provides a rigidfixation point when anatomical structures are not available or adequateto serve as an attachment point. Furthermore, the top loading attachmentpoint is typically faster and easier to assemble than the current wiringtechnology.

Referring now to FIGS. 10A-D and 13, the extender 105 can include anextension member 139 in the form of a rod 206 that defines a proximalend 206 a and a distal end 206 b opposite the proximal end along acentral rod axis 210, and a middle portion 206 c disposed between theproximal end 206 a ad the distal end 206 b. The rod 206 includes anengagement member illustrated as a loop 207 that is connected to theproximal end 206 a. The rod 206 further includes a bushing 150 that isretained in the loop 207 in the manner described above with respect tothe loop 142. The middle portion 206 c and the distal end 206 b can beangularly offset with respect to the loop 207 as desired. In thisregard, a kit of rods 206 can include define different angles betweenthe middle portion 206 c and/or distal end 206 b and the loop 207.

During operation, the extender 105 can connect a previously implanted ornewly implantable bone fixation element 22 to a previously-implantedtranslaminar screw. In particular, the locking cap 34 is removed, andthe tapered set screw 130 is coupled to the previously implanted bonefixation element 22 in the manner described above. The rod 206 is thenconnected between the bone fixation element 22 and the translaminarscrew by placing the bushing 150 around the middle portion 130 c of thetapered set screw 130 and the distal end 206 b into the rod seat of thetranslaminar screw. The translaminar screw can be constructed asdescribed above with respect to the vertebral implant 75, and is used tofix adjacent vertebrae and fuse them together as known in the art. Inparticular, the translaminar screw is inserted through the facets andlaminae of adjacent vertebrae in order to fix the adjacent vertebraetogether.

The locking nut 160 is then screwed down over the superior or proximalportion 130 a of the tapered set screw 130, thereby forcing the extenderrod 206 and the bushing 150 to advance distally with respect to themiddle portion 130 c of the tapered set screw 130 and, in so doing,forcing the bushing 150 to expand and match tapers of the interior ofthe bushing 150 and the exterior of the middle portion of the taperedset screw 130 to lock via an interference fit, as described above. Thelocking cap 34 of the translaminar screw is then screwed into the top ofthe anchor seat of the translaminar screw until the angular orientationof the bone anchor 30 of the translaminar screw is locked with respectto the anchor seat 26 of the translaminar screw so as to lock theextender rod 206 in to the translaminar screw assembly.

It should be appreciated that the extender 105 can connect at a firstend (including the polyaxial loop 207 and bushing 150) to thetranslaminar screw and can be rotate about the rod axis 210 along thedirection of Arrow 211 as well as about the central screw axis B alongthe direction or Arrow 213, thereby providing an additional degree offreedom with respect to a plate that does not provide polyaxialrotation.

Referring now to FIGS. 9-10D and 14A-B, the fixation system 100 can beconfigured to connect a bone fixation element 22 of a bone fixationassembly 20 that is implanted in the cervical region of the spine to anoccipital plate 250 that is configured to be fastened to the occiput253. The occipital plate 250 may assume a variety of forms known in theart, and can include a central body 257 that includes an engagementmember 252 configured to receive the distal end 141 b of the extenderrod 140. For instance, the engagement member 252 can include an apertureextending longitudinally through the central body 257 that is sized toreceive the distal end 141 b of the extender rod 140, and a set screwconfigured to lock against the extender rod 140. A pair of occipitalplates 250 is illustrated as fastened to the distal end 141 b of eachextender rod 140, each having respective plate sections 250 a and 250 bthat project outward and opposite each other from the engagement member252. Each plate section 250 a and 250 b can be independently rotatableabout the rod 140 or rotatably in unison about the rod 140. Additionallyor alternatively, each plate section 250 a and 250 b can flex about thecentral body 257. Each plate section 250 a and 25 b can include at leastone bone fixation aperture 255 extending therethrough that is sized toreceive a bone fastener 30, such as a screw or a hook, so as to securethe plate sections 250 a and 250 b to an underlying bone, such as theocciput.

During operation, a fixation assembly 20 is pre-implanted in thecervical region of the spine, such that the bone fixation elements 22can be implanted in respective underlying cervical vertebrae. Theextender 105 is attached to the cranial most bone fixation element 22,which can be newly implanted or implantable, or previously implantedinto a cervical vertebra C, after the locking cap 34 has been removed inthe manner described above (e.g., to the vertebral implant 75 of thecranial most bone fixation element 22). The second, rod-shaped distalend 141 b of the extender rod 140 is coupled to the occipital plate 250using any of a variety of attachment mechanisms known in the art. Inaccordance with the illustrated embodiment, the system 100 can includefirst and second columns 101 a and 101 b of fixation elements 22 andspinal construct extenders 105 that couple the cranial most fixationelement to an adjacent bone, which is illustrated as the occiput.

The top-loading polyaxial construct extender 105 enables the surgeon tohave hinged capability when connecting the occiput to the cervical spineto enhance surgical ease and flexibility. The extender rod 140 can beprebent at a desired angle with respect to the loop 142, and is shorterin length than the conventional hinged rods used for such applications.Accordingly, the top-loading polyaxial construct extender 105 is easierto handle and connect between the cervical spine and the occiput.Further, the use of the top-loading polyaxial construct extender 105allows a surgeon to build a cervical spinal construct and then decide ifit is desired to add occipital fusion hardware, whereas, conventionalhinged rods cause one to commit to instrumentation and hardware at thebeginning of surgery.

It should be appreciated that a plurality of revision connectorembodiments has been described herein. Thus a spine fixation revisionconnector kit can be provided that includes a plurality of revisionconnectors, each revision connector being configured to couple at leastone vertebral body to an adjacent bone, which can be another vertebralbody for example or can be the occiput. At least one revision connectora plurality of revision connectors in a revision connector kit defines adifference with respect to at least another of the plurality of revisionconnectors in the kit. For instance, the different revision connectorcan have a different length or construction of the polyaxial extensionmember 139. Alternatively or additionally, the screw 130 of thedifferent revision connector can be straight instead of tapered, suchthat the set screw 130 does not lock the bushing 150 in the respectiveloop, thereby allowing the bushing to articulate in the respective loopafter fixation. Alternatively stated, the loop 142, and thus thepolyaxial extension member 139, can pivot or articulate in the lockedposition relative to the screw 130 and vertebral implant 75 to which thescrew is fastened. Alternatively or additionally still, the distalportion 130 b of the screw 130 can include a borehole or a fullthroughhole that includes a distally disposed interior set of threadingthat is configured to engage a set of threading on the exterior of theanchor seat 26 of the previously implanted or newly implantablevertebral implant 75 so as to accommodate the variety of vertebralimplants or hooks that includes exterior threading configured for usewith interiorly threaded set screws or locking caps.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiment disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the present description.

We claim:
 1. A spinal construct extender configured to couple to a spinefixation rod, the spinal construct extender comprising: a fastener; anextension member having a body that defines a rod, the body having aproximal end, and an opposed distal end that is spaced from the proximalend along a first direction, the distal end configured to be received ina rod-receiving channel of a bone fixation element, an engagement memberthat extends from the proximal end of the body, the engagement memberhaving an interior surface that defines an aperture that extends throughthe engagement member; and a bushing insertable in the aperture, thebushing having an interior surface that defines a hollow interiorconfigured to receive the fastener such that the interior surface aengages the fastener to thereby couple the spinal construct extender tothe spine fixation rod, wherein the bushing is configured to enable theengagement member and extension member to pivot relative to the fastenerwhen the bushing is disposed in the aperture and the fastener isreceived in the hollow interior.
 2. The spinal construct extender ofclaim 1, wherein the body is bent at a location between the proximal endand the distal end.
 3. The spinal construct extender of claim 2, whereinthe body is bent so as to define an s-shape between the proximal end andthe distal end.
 4. The spinal construct extender of claim 2, wherein thebody is bent such that at least a portion of the distal end is lowerthan the proximal end along a direction that is perpendicular to thefirst direction.
 5. The spinal construct extender of claim 2, whereinthe body is bent such that an entirety of the distal end is lower thanthe proximal end along a direction that is perpendicular to the firstdirection.
 6. The spinal construct extender of claim 1, wherein thebushing comprises a superior surface and an inferior surface, whereinthe interior surface of the bushing extends between the superior andinferior surfaces.
 7. The spinal construct extender of claim 1, whereinthe bushing has a partially spherical external surface, opposite theinternal surface.
 8. The spinal construct extender of claim 7, whereinthe interior surface of the engagement member is partially spherical. 9.The spinal construct extender of claim 1, wherein the hollow interior ofthe bushing is configured to receive a fastener coupled to the spinefixation rod.
 10. The spinal construct extender of claim 1, wherein thebushing is polyaxially pivotable within the aperture.
 11. The spinalconstruct extender of claim 1, wherein the bushing is configured suchthat a position of the bushing is fixed by pressing an exterior surfaceof the bushing against the interior surface of the engagement member.12. The spinal construct extender of claim 1, wherein the distal end ofthe extension member is substantially cylindrically shaped.
 13. Thespinal construct extender of claim 1, wherein the hollow interiorextends through the bushing along a central axis, and the bushing has anexterior surface that is spaced from the interior surface of the bushingalong a direction that is perpendicular to the central axis.
 14. Thespinal construct extender of claim 1, wherein the fastener engages aspinal fixation rod so as to couple the spinal construct extender to thespinal fixation rod.
 15. The spinal construct extender of claim 14,wherein the fastener defines a distal portion that is configured toengage the spinal fixation rod, and a threaded proximal portionconfigured to be received in the aperture.
 16. The spinal constructextender of claim 15, wherein the threaded proximal portion definesexternal threading.
 17. The spinal construct extender of claim 1,wherein the hollow interior of the bushing is configured to receive thefastener when the bushing is received in the aperture of the engagementmember so as to couple the spinal construct extender to the spinefixation rod.
 18. The spinal construct extender of claim 1, wherein theextension member and engagement member are integral with one another.19. The spinal construct extender of claim 1, wherein the engagementmember extends from the extension member such that a central axis of theaperture is angularly offset from a central axis of the proximal end ofthe extension member.